The invention relates to a pushbutton tuner for a radio receiver, and more particularly, to a pushbutton tuner which achieves a precise tuning to a preset desired frequency associated with a particular pushbutton whenever the latter is driven to its operative position.
A pushbutton tuner is well known having a plurality of pushbuttons arranged to achieve a tuning to a plurality of preset frequencies so that whenever a particular pushbutton is driven to its operative position, a tuning to a corresponding frequency is achieved. Such a pushbutton tuner includes a plurality of manually operated slides in the form of flat plates which are arranged so that their surfaces are coplanar. Each of the slides is independently movable between its inoperative and its operative positions, and whenever one of the slides is driven to its operative position, a control member which is carried by the slide causes a displacement of a tuning element through a given distance, the element being disposed so as to be movable in a direction perpendicular to the direction of movement of the slide. The displacement of the tuning element operates an armature which is telescoped into a tuning coil of the tuner, thus achieving a tuning to a desired frequency. In order to realize a tuning to a particular frequency, the control member can be positioned relative to its corresponding slide and locked in position. Unless it is unlocked, the control member maintains its given orientation. The tuning element is formed with a plurality of notches one for each of the control members and which is adapted to be engaged by part of the control member corresponding to each of the slides. Usually, these notches are each formed as a pyramidal surface having one or two linear bevelled surfaces. When the part of the control member is engaged with the corresponding notch, and is driven along the bevelled surface of that notch in response to a force applied thereto, a component of the force causes the tuning element to move in a direction perpendicular to the applied force, with its movement continuing until it is constrained by the apex of the bevelled surface. The tuning element can also be controlled to a position corresponding to a desired frequency to be received by a manually rotatable knob which operates through a clutch. In this instance, if the unlocked control member is engaged with the apex of the corresponding bevelled surface, it can be positioned to provide a tuning to a particular frequency. When positioning the control member, the clutch maintains an operative connection between the rotatable knob and the tuning element, but is deactuated to interrupt the operative connection between the rotatable knob and the tuning element during a normal use when a selected slide is driven to its operative position in response to an operation of a pushbutton.
In the construction of such a conventional pushbutton tuner, each slide is slidably disposed in a slot formed in a baseplate or support plate and which guides the direction of movement of the slide. To support the slide in a slidable manner, the size of a slot must be greater than the outer profile of the slide in order to reduce the frictional resistance. However, an increased clearance between the slide and the slot may cause a rattling in the movement of the slide. When such rattling is present, if the control member is engaged with the apex of the bevelled surface in the notch which represents a reference position to provide a tuning to a desired frequency, the slide will be displaced by an amount corresponding to the degree of rattling, which displacement is transmitted to the tuning element to cause its misalignment. An error in the tuning accuracy of the tuning element will be caused even by a small displacement or rattling of the slide. If the pushbuttons are arranged to establish exact desired frequencies when the tuner assembly is initially calibrated, each subsequent operation of the pushbutton will result in a turning to an inaccurate offset frequency.
Investigations have revealed that in a pushbutton tuner of the type described, a displacement of the tuning element is caused principally by the use of a single tuning element, which displacement occurs in response to a component of the force applied to the control member even though the latter is engaged with the apex of the notch. Consequently, it is a task of the invention to provide an adequate accommodation of such component of the force.